Hydraulic piston pumps and motors



Nov. 29, 1966 Z. A. LOMNlCKl Filed Jan. 4, 1965 4 Sheets-Sheet 1 REPET ITION OF THE SHAPE IN (-60,"+60) REPET ITIoN OF THE SHAPE IN (-60360) c HA) \V// FIG, I. 4

\ o MIRROR 3O IMAGE VALUES o READ FROM TABLE 11 O 3O MIRROR o IMAGE 60 o FIG. 3.

LWQIIZOF Zbigm'eu) I /examjer' Lomniclfl' 8 KW UM M Z. A. LOMNICKI HYDRAULIC PISTON PUMPS AND MOTORS Nov. 29, 1966 4 Sheets-Sheet 2 Filed Jan. 4, 1965 Y= RNA) FIG. 4.

' InuenL w Z2) nieu) fl/exanaer Lavinia/ 1 5 Jam, [fluid Nov. 29, 1966 2. A. LOMNICKI HYDRAULIC PISTON PUMPS AND MOTORS 4 Sheets-Sheet 8 Filed Jan. 4, 1965 FIG. 5.

IHVBHZUF Zbigniew H/amnaler Lomnick; 5/ JM, J

fiflameys Nov. 29, 1966 z. A. LOMNICKI 3,287,993

HYDRAULIC PISTON PUMPS AND MOTORS Filed Jan. 4, 1965 4 Sheets-Sheet 4 FIG. 6.

' rmlen vr Zklgnieu) jg/exanaler Lbmniflki 5 MM, 726% v-mlw HIZOrns/s The present invention relates to track members for hydraulic piston pumps and motors.

In the specification of our co-pending United States patent application Serial No. 252,128, filed January 17,

1963, hereinafter referred to as the parent specification,

there is described and claimed a track ring for a hydraulic pump or motor of the radial piston type having five or more pistons, in which ring part of the section of the running surface thereof is the locus of the end of a radial line rotating about the centre of the basic circle as defined therein, the length of the line being C+ (A), where C is the radius of the basic circle and A is the angle between the radial line and the bisector of the angle subtended by an arbitrarily chosen working sector as defined therein and in which (A) is defined by the following conditions:

in which conditions R'is the lift of the pistons, 20: is the angle subtended at the centre of the basic circle by the limits of the working sector, and on is defined by a=(lll).1r/2n if n is odd, and by a=(n2).1r/2n if n is even, where n is the number of pistons, the remainder of the section of the running surface being a mirror image of the above function.

There is also defined and claimed a similar arrangement but having S working strokes per revolution, wherein (A) is compressed S times so as to assume its complete cycle of values S times per revolution.

The parent specification is applicable only to hydraulic pumps or motors of the radial piston type having five or more pistons.

We have now succeeded in making the invention applicable to three or more pistons and also to hydraulic pumps or motors of the axial piston type and of the linear movement type.

Pumps and motors of these types are known in which the rate of movement and volume rate of flow are not strictly proportional, resulting in an irregular pump delivery or uneven motor torque or force, as the case may be, even when the pump is driven at a constant rate or f(A)=R for org/s5 the motor is supplied with the liquid at constant pressure. 7

-United States Patent 0 ice of a radial line rotating about the centre of the basic circle as defined below, the length of the line being C+ (A) where C is the radius of the basic circle and A is the angle between the radial line and the bisector of the angle subtended by an arbitrarily chosen working sector as defined below, and in which f(A) is defined by the following conditions:

sin -1r for 133A so:

in which condition R is the lift of the piston between R and +R, 2a is the angle subtended by the working sector extending from a to +a, and 2B is the angle subtended by that part of the working sector over which the distance C+ (A) of the track ring from the centre of the basic circle is proportional to the angle, i.e. over which the track ring forms a part of a simple spiral, and in which the various sets of values a and B to be applied are specified in Cases H, III and IV of Table A below, Case I having been covered in the parent specification, Table A being taken to extend also to such pumps and motors as are specified by provisos (a) and (b) below, the remainder of each cycle of the said section being a mirror image of the above function.

In one embodiment of the present invention there is provided a cam or track member in the form of a rack for relative linear movement for linear hydraulic motor or pump arrangements where the specific track shape, including Case I of Table A, calculated in accordance with the formulae for f(A) above can equally well be treated as the track shape of the said rack by treating the polar co-ordinates r, A (where r= C+f(A)), as Cartesian coordinates, y, x, respectively. Other terms take the appropriate and obvious definitions, remembering that angles a, {3 become abscissae.

In another embodiment of the present invention there is provided a cam or track member for hydraulic pumps or motors of the axial piston type having three or more pistons, in which the specific track shape, including case I of Table A, calculated by using the Cartesian co-ordi nates as indicated above, can equally well be treated as the track shape of a cylindrical cam or track member by relating the Cartesian co-ordinates to cylindrical co-ordinates, r, 0, z, wherein y=C+f(A) becomes 2,, and x becomes the circumferential distance (r0) from an arbitrary initial radial line, such that the new independent co-ordinates 0 takes the values of the old independent co-ordinate A and r is constant.

The invent-ion will first be described as it relates to the radial piston type of pump or motor.

The cross-section of the running surface of the track ring of the present invention differs from a true circle, hereinafter called the basic circle by amounts which are functions of the angle A defined between a radial line rotating about the centre of the basic circle and the bisector of an arbitrarily chosen working sector as defined below.

The dwell sectors are those sectors of the basic circle between the limits of which d/dA (C+f(A))=O, and the 5 fluid at a constant pressure. The volume of flow deworking sectors are the sectors lying outside the dwell manded by the motor will also be uniformly proportional sectors. The spirality sector is that part of the working to the rotational speed of the motor and vice versa for a sector between the limits 5 and +5 of which d/dA pump. (C+ (A)) is a constant r2R/ (ix-H6). The track ring design to produce the above features is The formulae for f(A) hold true for 71/ 2 A 1r/ 2, i e. 10 dependent upon the number of pistons and upon the numover one semi-circle; and for the interval 1r/ 2 to 31r/2, i.e. ber of strokes in one revolution of the pump or motor. for the remaining semi-circle, (A) is defined as f(1r-A), The track ring contour is derived as a function of anguthus becoming a mirror image of the function in the first 13f position, to be added to or subtracted from the basic sgmi.circ1e V circle. It s dependent upon the number of pistons and Table A gives the four possible cases with respect to 15 pon the P dwell and spirality sectors, and indicates the (alternative) T e radius of the basic circle C, the piston lift R and conditions imposed on the number of pistons n, and gives the rate of Iotatlon, control the P P g fate of h P p the values of the remaining angles where appropriate, corr th torque of the motor. If this can be achiev d by responding to each case, for a pump or motor having one a Plstoh 1 0116 Stroke P l'evohltloh, h 3 P p stroke per revolution. Thus the various possible sets of of motor h 2, h Strokes P revolution h the values of the angles a, 13 and A, according to the number S e rate of rotation will produce the Sa e P p ra of pistons, are set out in Table A, where 6=1r/2a is the fq Provided the Plstol1 lift 18 reduced P P angle corresponding to a half of the dwell sector. y R/ F 3 Cases H and III produce a constant torque but have no The deslghs y the addltlhha'l P y of dwell periods during which the rate of piston movements Prhdhclhg Plstoh hccetetatlohs nuous funCt1 0n would be zero. Solutions given in Case IV allow arbiand consequently Provldlhg Telatlvely Smooth operatlohtrary values of dwell region to be introduced provided that Moreover, P p and motors haVlIlg e mlmhel: of they are small and considerably below the limits given in htrokes Phf revolutloh and the f 0t Plstohs ythe last column of the table; these dwell regions may be 8 cohdlltlohs f Wlth the Value d greater necessary in some circumstances to improve the design of 30. than 1 W111 be designs In Whlch e resultant forces form the pump or the motor, 3 P h p Th formula above r fe to Pumps of motors with Theumproved track ring design can further be applied one stroke per revolution and n pistons. Pumps and to Y h 'y Pumps and q motors with more than one, say S strokes per revolution agalh Wlth the advantage of o mg lr egularities in and n pistons have also the required property provided the :p p moth! l In S case the Plsttms of that the pump or motor co-operate with a three-dimensional (a) The number of pistons n divided by the highest track Surface comprising a Ph y of axially-Spaced common factor d of n and S i.e. the reduced number track rings of e P F h'lVehtwh, smoothly t gfi of pistons n =n/d satisfies one set of the conditions set Q Q W thls embvqlment the {hfixlmum Plstoh out i T bl A and 40 lift R is a function of the longitudinal position of the track (b) For the track Ting corresponding to "1 pistons, surface relatively to the plane of the pistons. By relative f(A) is contracted into S working sectors, each S times dlsplacemmtt of the track surface penPend1cI.1lar1y to thls Smaller than the working Sector in the case of om Stroke plane the pistons move around effectively ditferent track rings so that the pump delivery or motor torque can be l per revolution. In other words, a new track ring 15 defined in this case by the formula for the radial len th vanedm any deslred manner The choice of the number of pistons is determined by C+g(A) Y (A) :flSA) and KA) assumed to the requirement of the pump or motor. The torque of a have a period of 21r. When A ranges from 0 to 211-, A motor is given by piston area multiplied by the product ranges from 0 to 21r/S and, for S strokes per revolution, f n S and R and thus for a given output torque, these the same movements of the pistons relatively to the basic items may be varied as desired Provided that the final circle are repeated S times per revolution. roduct i unaltered.

TABLE A case Description Conditions, fhgiipiggg :11 number Value of the remaining angles I Positive dwell 6 0 11. even 26 a: (n 2)7r/2n 6:11

N o spirality sector fl=0 n odd Z5 6=(n-1)w/2n 6=1rl21i II No dwell 6=0, a=1rl2 N o spirality sector fl=0 n even 24 HI No dwell 5=0, a=1rl2 n=fi g=,.-/

Positive spirality sector fi 0 11, even 28 d ble b 4 B n/:1; or 21r/n ifiii diiliiue hi? 4; 2:52.67,

71V Small dwell 6 -0, a 1r/2 5 77' even zqgigvgggf3ggy 4 Of the following two tables, Table B gives the angles [8 of the spi-rality and the angles A of the dwell sectors corresponding to the number of pistons of a pump or motor having one working stroke per revolution, and Table C gives the radial distances from the centre of the basic circle to the track ring of a pump or motor with 11:33 pistons,

R=1 unit and C= units. are given in degrees.

In Table B both p and A at the centre of the basic circle by the limits of each dwell sector is 26.

TABLE B Number of pistons n Casrse IOII Angle B 30--- 54 30- 129i"--. 22% or 45..-- 30..." 18 or 36.

Case IV Angle a a0+s-- 54+a-- 30+5 129t+a 45+5 30+a- 18+5.

5 0 Angles5lessthan 30 1s 30 3856"- 22% 30 30.

TABLE 0 FIGURE 2 illustrates the shape of the track ring of which the measurements are set out in Table C. This track Angular Radial Radial l position Position lift dimension dimension 2 ls 91. q or mqtor aving three p a plstpn cm at (A) o at lift of one unit, and a basic c1rc1e of radius ten umts, the working sector subtending an angle of 180, from Aindegrees 1 a C+]'(A) (3- f(A) 0 which 2 30=60 is the spirality sector while 2 60 =120 corresponds to the remaining parts of the working 0 0. 000000 10. 0000 10. 0000 sector. In this example of Case III the dwell sector is non- 8938883 are 2-220 existent- 9 01150000 1011500 9:8500 FIG. 3 is derived as follows. In the case of motors lg g-gggggg lg gggg Egg 25 or pumps with S strokes per revolution the angles given 13 0. 300000 10.3000 9.7000 in Table B furnish the necessary data provided that the g; Egggfl igjggg ggggg values 1n the top row, (i.e. the number of p1stons n are 27 0.450000 10. 4500 9.5500 taken as values of n =n./S, i.e. where n has been divided 3g 3 22828? $2 88 3:38? by S to obtain the values in this top row. Similarly the 30 0 599182 10.5902 9. 4008 30 values glven in Table C for n=3, S=1 define automaticalig ggggig 235 3:235; ly the shape of the track ring tfOI any other admissible 45 0 737540 10. 7375 9. 2025 number S of strokes per revolutlon provided that the numg? 352 233 $5123 8: bers of the first column (angular position) are divided 55 0. 851365 10.8514 9.14g0 by S. Thus in the case n=9, S=3, the highest common 26 8 333;??? igfi; 3:3 factor d is 3, so that n =9/3=3 and the angulanposr- 03 0. 932195 10.0322 0. 0678 trons should be divided by S=3 so that the radial dimen- 28 832%; $132, 3 318 sions of the track range from 9.0000 at 30 to 11.0000 22 0. 972 759 10.9788 9. 021; at +30. The radial dimensions thus obtained for the t5 8333523 8 $1335 3:85. 40 sector (30 to +30) are extended as mirror images 81 0.33335 1 .3353 3. 2; to the sectors (60" to 30) and (30 to 60) this 2 81 mjgggg 910001 shape (-60 to +60") is repeated twice more 60 90 1.000000 11. 0000 9.0000 to +180"), (180 to 60) and fills the whole c1rc1e.

This is what is shown in FIG. 3.

The nomenclature describing the track ring will now be explained with reference to the drawings in which:

FIG. 1 is a diagram showing the basic circle and a track ring contour based thereon, to indicate the extent of the various sectors;

FIG. 2 is a polar diagram of a track ring having the measurements set out in Table C;

FIG. 3 is a diagram showing the basic circle and a track ring contour based thereon having three strokes per revolution;

FIG. 4 is a diagram, showing a basic straight line and a cam or tracking member contour based thereon, being the shape of a linear moving rack in a linear hydraulic motor or pump arrangement;

FIG. 5 shows a partially cut away end view of a motor having seven pistons, the track ring providing four strokes per revolution and the running surface thereof depicted diagrammatically; and

FIG. 6 shows a section along the line xx of FIG. 5.

In FIG. 1, the basic circle 1 is shown in full lines and the track ring contour 2 is shown in broken lines. This latter consists of two lobes, one inside and one outside the basic circle. The lines 3 mark the boundaries between the working and dwell sectors. Lines 4 mark the boundaries between the spirality sector (5 to +5) and the remaining part of the working sect-or, the mirror images of lines 4 in the left hand side of the diagram not being shown in FIG. 1.

As shown, each working sector Subtends an angle of 20a at the centre of the basic circle 1, having a radius C. The distance from the centre of the basic circle to a point on a track ring contour is C+f(A). The angle subtended Reverting now to one of the other aspects of the invention mentioned originally, i.e. the linear hydraulic motor or pump arrangement, FIG. 4 is derived as de scribed above by means of a change to Cartesian co-ordinates. L is one track cycle and is an arbitrary dimen sion depending upon the precise values of constant rack force and velocity concerned. R is the lift of a piston. X and Y are the co-ordinates of a point on the track where X =LA/ 360 and Y=Rf(A). This means that the abscissae measurements are proportional to the original arc length Zn-CA/ 360 and the ordinate measurements to C+f(A). It follows that the cam shape, repeated on the rack outline the requisite number of times, dependent on the linear travel required, can be applied to a linear hydraulic motor or pump in :which the movement of the pistons at right angles to the length of the rack arrangement produces relative lengthwise movement between the rack and the piston-carrying member.

By arranging n pistons in the sector covering one cam cycle a linear hydraulic motor can be constructed which produces a constant longitudinal component of force and a constant rate of rack movement when the pistons are subjected to constant fluid supply pressure, and vice 'versa for a linear hydraulic pump. An additional advantage is that the output force can readilly be increased by suitably providing extra blocks, of n pistons each, for example, as a linear continuation of the original block on a single cam form rack, or again for example on the opposite side of a double cam form rack.

The features of the radial piston type of pump or motor indicated above apply similarly to the axial piston type except for the change in shape indicated above by the change of co-ordinate system, and the consequent additional considerations noted below.

The improved track design according to the invention can be applied to any of the stated types of variable delivery pumps or variable torque or force motors, as the case may be. In general terms, to achieve this, the pistons of the pump or motor co-operate with a three-dimensional track surface comprising a plurality of spaced tracks according to the present invention, smoothly merging into each other, being spaced along the direction which is perpendicular both to the reciprocation axis of each piston and to the direction of working movement of each (piston) cylinder relative to the track member. In the case of the radial piston type the spacing is along the axis of rotation, as mentioned above. In the case of the linear movement types the spacing is perpendicular both to the linear movement and to the axis of each piston, i.e., to the x and y directions respectively, mentioned above. In the case of the axial piston types the spacing is radial, but while radial adjustment of the (piston) cylinders is more difficult to achieve technically, there is the advantage of being able to vary the mechanical advantage of the slope on which the piston bears while keeping constant the force, torque and stroke of the piston, an important consideration for frictional losses.

The motor illustrated in FIGS. and 6 has seven pistons each performing four strokes per revoltuion. The motor comprises a casing 12 closed by an end cap 14, in which is mounted a main shaft 16 rotatable in roller journal 18 and ball journal 20. The main shaft 16 is connected to the cylinder block 28 by a coupling member 22 secured to the shaft by ring 23, intermediate coupling member 24 and a coupling member 26 connected to the cylinder block 28 by screws 29. The cyilnder block bears against an end bearing plate 30, and is rotatable about a distributor 32, through the centre of which passes the main shaft 16. Seven pistons 34 are mounted for radial reciprocation in the cylinder block 28 and carry trunnions 36 on which are mounted rollers 38 for bearing on two track rings 40, which are spaced apart by spacers 42. An oil seal 44 is provided between end cap 14 and casing 12. An oil seal 46 is held on shaft 16 by gland 48 mounted on end cap 14. The distributor 32 contains four flow and and four return passages 50, interconnected respectively by flow and return passages 52 in the housing, connecting to a flow inlet 54 and return outlet 56, FIG. 5.

In operation, a hydraulic medium supplied to inlet 54 passes through the flow passages 52 and 50, and into those of the cylinders connecting with these passages by virtue of the instantaneous position of the cylinder block 28. The pistons 34 in these cylinders are therefore urged outwardly and, bearing against the track rings 40, cause the cylinder block 28 to rotate counter-clockwise (FIG. 5) by reaction. Those cylinders connecting with the return passages 50 and 52 wil return the hydraulic medium forced out of them by virtue of reaction between their pistons and the track rings 40, to the outlet 56. If the roles of the inlet 54 and outlet 56 are interchanged the cylinder block will rotate the opposite way. Either motion is conveyed to a gear mounted at the end of the main shaft 16.

The formula given for the running surface of the track member only applies to the profile of the track member in the ideal condition when the outline defined by that profile corresponds to the path which a point on the central longitudinal axis of a piston would take assuming the piston was moved relative to the track member along the path which the track member would constrain the piston to take. In the event, for example, of a roller follower being used as in the embodiment of FIGS. 5 and 6, the above mentioned ideal condition is not obtained. In order for the piston movement to be that required, the profile is shaped so that the formula would apply to the surface which would be traced out by the central longitudinal axis of each roller 38 if the roller was moved along the profile, and it is this surface which would constitute the running surface of the track member. The

profile would be produced by using a milling cutter of the same diameter as the roller 38 and constraining the cutter centre to move along the ideal running surface profie given by the formula.

I claim:

1. In a machine having at least three pistons, the improvement comprising a track member having a cam surface in driving connection with each of said pistons, said cam surface comprising a pair of half peripheral sections, one of said half sections being a mirror image of the other half section, and one half section being shaped such that, assuming a motion of each of said pistons along a path determined by said cam surface, a point passing through the central longitudinal axis of each of said pistons would have an axial displacement f(A) from the medial position of the piston, where A is the relative displacement, having one working stroke in the range lying between 0 and Zr, and where f(A) is defined by the following conditions:

f(A)=R for (is/A5 in which conditions 2R is the stroke of the piston, 2a is an arbitrarily chosen working section within the range of A and 25 is the range of A within the working sector throughout which the displacement (A) is a linear function of A, and in which one of the three separate sets of values a and B to be applied are those hereinbefore specified in Table A as Cases II, III and IV.

2. The improvement of claim 1 wherein there are S working strokes in the range lying between 0 and Zr, the axial displacement of said point of each of said pistons from its medial position being g(A), where g(A)= (SA) and (A) is defined by the conditions set out in claim 1, and the function g(A) and its image being repeated S times in each range of 21r, in which the quotient of dividing the number of pistons n by the highest common factor. d of n and S satisfies one set of the conditions set out in Table A.

3. The improvement of claim 1 wherein said track member has a three dimensional cam surface of which the section that contacts the pistons during said relative movement changes in shape in the direction normal to the directions of reciprocation and said relative movement such that the surface is able to be displaced along the normal relatively to the pistons to vary the output of the machine.

4. The improvement of claim 1 further comprising follower means coupled to one end of each of said pistons and cooperating with the cam surface of said track member, and wherein the center of said follower means behaves precisely the same as said point.

5. The improvement of claim 4 wherein said follower means comprises a roller.

6. In a radial piston type machine having at least three pistons, the improvement comprising a track ring-having a cam surface in driving connection with each of said pistons, said cam surface comprising one circumferential section and thereby complementary to one stroke of each of said pistons per revolution of said pistons and track ring relative to each other, one half of said section being a mirror image of the other half, and one of said section halves being shaped such that, assuming a motion of each of said pistons around the center of said track ring along a path determined by said cam surface thereof, a point on the central longitudinal axis of each of said pistons would trace out an arcuate pattern, being the locus of the end of a radial line rotating about the center of the basic circle as defined below, the length of the line being C+ (A) where C is the radius of the basic circle and A is the angle between the radial line and the bisector of the angle subtended by an arbitrarily chosen Working section as defined below, and in which (A) is defined by the following conditions:

f(A)=R for aSAS-g in which condition R is the lift of the piston between R and +R 20a is the angle subtended by the working sector extending from a to +a, and 2,9 is the angle subtended by that part of the working sector over which the distance C+f(A) of the track ring from the center of the basic circle is proportional to the angle, i.e. over which the track ring forms a part of a simple spiral, in which the various sets of values a and B to be applied are specified in Cases II, III and IV of Table A.

7. The improvement of claim wherein there are S working strokes in the range lying between 0 and 211-, the

length of said radial line being C+g(A) where g(A)=f(SA) and (A) is defined by the conditions set out-in claim 5, and the function g(A) and its image being repeated S times in each range of 21r, in which the quotient of dividing the number of pistons n by the highest common factor d of n and S satisfied one set of the conditions set out in Table A.

8. The improvement of claim 6, further comprising roller follower means coupled to one end of each of said pistons and cooperating with the cam surface of said track member, and wherein the center of said roller follower means behaves precisely the same as said point on the central longitudinal aXis of each of said pistons.

References Cited by the Examiner UNITED STATES PATENTS 2,101,829 12/1937 Benedek.

2,595,479 5/ 1952 Nelson.

3,046,950 7/1962 Smith 103174 X 3,099,223 7/ 1963 Mercier 103161 OTHER REFERENCES DAS 1,007,707, May 1957, Germany.

FRED C. MATTERN, IR., Primary Examiner.

BROUGHTON G. DURHAM, MILTON KA'UFMAN,

Examiners. D. H. THIEL, Assistant Examiner. 

1. IN A MACHINE HAVING AT LEAST THREE PISTONS, THE IMPROVEMENT COMPRISING A TRACK MEMBER HAVING A CAM SURFACE IN DRIVING CONNECTION WITH EACH OF SAID PISTONS, SAID CAM SURFACE COMPRISING A PAIR OF HALF PERIPHERAL SECTIONS, ONE OF SAID HALF SECTIONS BEING A MIRROR IMAGE OF THE OTHER HALF SECTION, AND ONE HALF SECTION BEING SHAPED SUCH THAT, ASSUMING A MOTION OF EACH OF SAID PISTONS ALONG A PATH DETERMINED BY SAID CAM SURFACE, A POINT PASSING THROUGH THE CENTRAL LONGITUDINAL AXIS OF EACH OF SAID PISTONS WOULD HAVE AN AXIAL DISPLACEMENT F($) FROM THE MEDIAL POSITION OF TH E PISTON, WHERE $ IS THE RELATIVE DISPLACEMENT, HAVING ONE WORKING STROKE IN THE RANGE LYING BETWEEN 0 AND 2$, AND WHERE F($) IS DEFINED BY THE FOLLOWING CONDITIONS: 